The mouse core will support the various components of the program in two major ways: a) the preparation of transgenic and gene knockout mice; and, b) the maintenance of various mutant mouse lines to be used in the proposed studies. A major initial focus of the core will relate to the creation of both protein 4.1 knockout mice and mice expressing various protein 4.1 transgenes. The proposed studies to dissect in vivo the biological functions of protein 4.1 are described in projects 1, 2, 3, and 6. The core will play a central role in assisting the participating programs in designing the various aspects involved in of the murine studies. All the technical steps in creating the transgenic and gene knock- out mice (i.e. creating the various DNA constructs and performing embryo manipulations) will be carried out as part of this core. The core will also maintain and provide thalassemic mice.